1. Field of the Invention
The present invention relates to a bonding device, and more particularly, to a bonding device for fabricating a liquid crystal display device and a substrate for fabricating a liquid crystal display.
2. Discussion of the Related Art
In general, various flat panel type displays, such as liquid crystal display (LCD), plasma display panel (PDP), electro-luminescent display (ELD), and vacuum fluorescent display (VFD), have been developed to replace conventional cathode ray tube (CRT) devices. More particularly, LCD devices have been commonly used for their high resolution, light weight, thin profile, and low power consumption. In addition, LCD devices have been implemented in mobile devices, such as display monitors for notebook computers, and have been developed for computer displays and television monitors in order to receive and display broadcasting signals.
Various processes are commonly used for fabricating an LCD device. One process for fabricating an LCD device according to the related art involves a liquid crystal injection method that includes steps of forming a sealant pattern on one of a first and second substrate to form an injection inlet, bonding the first and second substrates to each other within a vacuum processing chamber, and injecting liquid crystal display material through the injection inlet. A second process for fabricating an LCD device according to the related art includes a liquid crystal dropping method which is advantageous over the liquid crystal injection method. liquid crystal dropping method. The liquid crystal dropping method is disclosed in Japanese Patent Application Nos. 11-089612 and 11-172903, and includes dropping liquid crystal material on a first substrate, arranging a second substrate over the first substrate, and moving the first substrate close to the second substrate within a vacuum state, thereby bonding the first and second substrates to each other. In the liquid crystal dropping method, steps of forming a liquid crystal material injection inlet, injecting the liquid crystal material, and sealing the injection inlet, are unnecessary since the liquid crystal material is predisposed on the first substrate.
FIG. 1 is a cross sectional view of a substrate bonding device according to the related art during a loading process. In FIG. 1, the substrate bonding device includes a frame 10, an upper stage 21, a lower stage 22, a sealant dispenser (not shown), a liquid crystal material dispenser 30, a processing chamber including upper and lower processing units 31 and 32, a chamber moving system 40, a stage moving system 50, an alignment system 70, and a vacuum pump 60. The sealant dispenser (not shown) and the liquid crystal material dispenser 30 are mounted on a side of the frame 10, whereby the bonding process of the frame is carried out.
The chamber moving system 40 includes a driving motor driven to selectively move the lower processing chamber 32 to a location where the bonding process is carried out, or to a location at which outflow of the sealant occurs. The stage moving system 50 includes a driving motor driven to selectively move the upper stage 21 along a vertical direction. The vacuum pump 60 is connected to a duct that is connected to an interior of the upper processing unit 31. Accordingly, when the upper and lower processing units 31 and 32 are connected, the vacuum pump 60 can reduce a pressure in the interior of the processing chamber.
The alignment system 70 includes an alignment camera for verifying an alignment state between a second substrate 52 attached to the upper stage 21 and a first substrate 51 attached to the lower stage 22, and is fixed to an upper surface of the upper processing unit 31. In addition, the alignment system 70 includes a transparent glass 31a installed within the upper processing unit 31 to allow the alignment camera to verify the alignment state between the first and second substrates 51 and 52.
FIG. 2 is a cross sectional view of the substrate bonding device according to the related art during the bonding process. In FIG. 2, the second substrate 52 is loaded onto the upper stage 21, and the first substrate 51 is loaded onto the lower stage 22. Then, the lower processing unit 32, having the lower stage 22, is moved into a processing location by the chamber moving system 40 for sealant dispensing and liquid crystal material dispensing. Subsequently, the lower processing unit 32 is moved into a processing location for substrate bonding by the chamber moving system 40. Thereafter, the upper and lower processing units 31 and 32 are assembled together by the chamber moving system 40 to form a vacuum tight seal, and the vacuum pump 60 is driven to maintain a vacuum state within the space defined between the upper and lower processing units 31 and 32.
The upper stage 21 moves downwards to reach a location whereby a position alignment between each of the first and second substrates 51 and 52 is to be carried out. Then, the alignment system camera 70 verifies alignment marks on the first substrate 51 loaded onto the lower stage 22 and the second substrate 52 loaded onto the upper stage 21. The alignment system camera views the alignment marks through the transparent glass 31a formed on the upper processing unit 31 and an opening 21a formed on the upper stage 21. After reading data corresponding to the alignment marks transmitted by the alignment camera 70, a position alignment process of the first and second substrates 51 and 52 is performed.
During the position alignment process, any misalignment amount between the first and second substrates 51 and 52 is verified by the alignment system camera 70, and is converted into a tilt amount. The stage moving system 40 is controlled according to this converted tilt amount, thereby compensating for the misalignment amount between the first and second substrates 51 and 52.
Once the position alignment process is complete, the stage moving system 50 moves the upper stage 21 to a lower location, thus closely contacting the substrate 52 loaded to the upper stage 21 with the substrate 51 loaded to the lower stage 22. Then, pressure is continuously applied to the first and second substrates 51 and 52, thereby performing a bonding process of the first and second substrates 51 and 52 and completing the fabricating process of the liquid crystal display.
However, the above-described bonding device according to the related art has the following disadvantages. With the advent of large-sized liquid crystal displays, the current bonding devices include a plurality of liquid crystal displays, each fabricated by bonding a pair of substrates. Thus, the position alignment between each substrate has become increasingly more critical. More specifically, when two misaligned substrates are bonded together, each cell area formed on each substrate cannot be accurately bonded to its corresponding cell area. Accordingly, the alignment of each cell area is highly dependent upon an overall alignment of the substrates.
In addition, as the number of cell areas formed on each substrate increases, the position alignment between each substrate should be carried out with more accuracy. However, in the bonding device according to the related art, alignment marks are formed only on two diagonal corner regions of each substrate, therefore an accurate position alignment cannot be carried out in regions without an alignment mark. Accordingly, as the size of a substrate becomes larger, the process of bonding two substrates becomes increasingly more critical.
Finally, since accurate alignment only occurs on the diagonal regions on each substrate, misalignment may occur in the remaining cell areas on the substrates, thereby causing a minor error difference. However, in the bonding device according to the related art such error differences are not compensated. Moreover, the bonding device according to the related art is problematic when carrying out a mass production of liquid crystal displays by bonding large-sized substrates having a plurality of cell areas.